Snap action switch



Jan. 6,1953 J. A. SPINA ETAL 2,624,819

SNAP ACTION SWITCH Filed Jan. 10 1951 Inventors: James A.Spina, Edward O. Anders en W xm Th eir' Attorney.

Patented Jan. 6, 1953 2,624,819 SNAP ACTION swrron James A. Spina, Schenectady, and Edward 0. Andersen, Ballston Spa, N. Y., assignors to General Electric Company, a corporation of New York Application January 10, 1951, Serial No. 205,282

13 Claims. 1

Our invention relates to snap action devices,"

and more particularly to snap action devices of the reversible dished type and especially suitable for use in thermostatically operated switches.

Internally stressed snap-acting devices of the dished type may be made of homogeneous spring metal and actuated by external force, or may be formed of bimetal and actuated by thermal self-deformation. Heretofore snap acting thermostatic devices of the dished composite metal over-center acting type have been particularly diflieult to manufacture, and those types which most readily adapt themselves to the manufacturing process have not been of a form which facilitates the inclusion of adjustable means for controlling the critical temperature.

In addition to facility of manufacture and ease of adjustment, it is highly desirable that such switches, particularly those of the thermostatic type, demonstrate a "no zero action in operation. By no zero it is meant that a positive contact pressure is maintained until such time as there has been initiated an overcenter action which is irreversible even though further application of the actuating influence is withheld. Thus at the time that the contact pressure becomes zero the device is in a transient and self-completing condition ofv operation, so that the contacts cannot be stopped in a dead center position of zero pressure.

Accordingly, therefore, it is a general object of our invention to provide a new and improved snap acting device of the internally stressed spring plate form which permits ready inclusion of adjusting means.

It is a further object of our invention to provide a new and improved snap acting thermostat of the dished internally stressed over-center acting type which is simple to manufacture and is readily provided with accurate and dependable temperature adjusting means.

It is another object of our invention to provide a new and improved snap acting switch of the internally stressed spring plate type which demonstrates a no zero action.

It is still another object of our invention to provide a new and improved snap acting thermostatic switch of the no zero type.

A still further object of our invention is the form we provide a substantially U-shaped split ring, or blade, of spring material curved flatwise and having opposite its juxtaposed ends a substantially U-shaped re-entrant arm which carries at its inner end a movable contact. The blade is mounted at its juxtaposed ends in a mounting bracket which hold the juxtaposed ends in cambered relation and deforms the blade into a dished formation, so that the central arm is angularly displaced outwardly on the convex side of the blade. When the blade is formed of bimetal it is so deformed that the high expansion metal is on the normally concave side of the dish. In order to provide adjustment of the critical point at which such a blade, or plate, reverses its concavity when actuated means are provided for holding the juxtaposed ends of the U-shaped blade in abnormal spaced apart relation, and this later holding means is adjustable.

In order to ensure a no zero snapping action the blade is formed with weakened portions of reduced transverse cross section at the points of connection between the side arms and the re-entrant central arm. The internal stress in the plate resulting from both the camber and the abnormal spacing of its juxtaposed ends is concentrated in these relatively weak sections, so that the ring has a greater transverse curvature at these points than at any other point. Thus when actuated over center, by external pressure or by heating, the side arms of the ring, having a relatively slight transverse curvature, first reverse their curvature, and this overcenter snapping action irreversibly induces a similar over-center snapping action at the weakened sections. Thus the blade maintains a positive pressure until a part of the blade has snapped over-center and irreversibly initiated a complete operation.

Our invention itself will be more fully understood and its various objects and advantages further appreciated by referring now to the following detailed specification taken in conjunction with the drawing, in which Fig. 1 is a side elevational view of a snap acting electric switch embodying my invention; Fig. 2 is a transverse cross-sectional view of the same switch taken along the line 2-2 of Fig. 1; Fig. 3 is a fragmentary cross-sectional view taken along the line 3-3 of Fig. 1; Figs. 4 and 5 are cross-sectional views of the switch blade taken along the lines AA and BB respectively of Fig. 2; Fig. 6 is a side elevational view of a snap action thermostatic switch embodying our in- Referring now to the drawing, and more particularly to Figs. 1 to 5 inclusive, we have shown a manually operable snap acting electric switch comprising a base I having mounted thereon a stationary contact 2 and a snap acting switch blade 3 carrying a movable contact I. The

switch blade 3, as more clearly shown .at-Fig.- -2,:-. is formed from a normally flat sheet of resilient metal and shaped as a split ringhaving a :substantially U-shaped re-entrant' contact carrying arm to disposed opposite the juxtaposed ends of the ring and between the side arms thereof.

The blade 3 has weakened .portions .of reduced; transverse section at each side of the,..central.. arm 3a where this arm. .joins the side arms of the blade, as at the sections BB, Fig. 2. The blade, or plate, 3 is mounted upon the base! in cantilever fashion by a bracket 5 which engages the juxtaposed ends of the side arms. A- manually operable push rod 6 is mounted upon the base i and arranged to engage the side arms of the blade 3 to actuate the switch.'- Itwill be understood that this push rod may: be: operated by any suitable slow-acting temperature responsive device.

As illustrated at Fig. 3, the-mounting-bracket 5 is formed as a U-shaped clamp having -op-= positely outwardly turned ears 5a and 5b ex-' tending from the ends of its side arms, andhave ing its side arms tied together by means of: an adjusting bolt 1. The outwardly extending ears 5a and 5b are slightly cambered with respect to each other and about the axis of symmetrybf the blade 3 (i. e. thelongitudinal axis-of the inwardly extending arm 30.). The juxtaposed ends of the side arms of the blade 3 are'fastened to the oppositely outwardly-extending.ears:5a and 5b of the mountingbracket 5, asbywelding, and are thus held in camberedrelation; This is clearly illustrated at- Figs. 1 and ..3.. The mounting bracket 5 is shownfixed to. theplate I by means of a bolt 8 through the bightportion of the bracket.

With the side arms ofsthe; blade .3 -held;.in eambered relation at their juxtaposed ends as shown at Figs. 1 and. 3, the. blade. itself is-ine ternally stressed and deformed into. a dished: for.- mation, so that the inwardly extendingcentral arm 3a is angularly displaced outwardly. from the normal plane of the blade and towardsthe convex side of the blade in its dished form. In this position the contact 4 is in-engagement-with the fixed contact 2.

In order to strengthen the over-centerxsnanping action of the switch blade 3, the.-.bolt-...'I is either drawn up or backed off;.:thereby to hold the juxtaposed ends of the switch plate in an abnormal spaced apart relation andfurther to internally stress the blade. Such'addi-L tional internal stress is concentrated primarily in the weak portions of reduced cross section at the top of the plate. Moreover the snapping action of the plate is rendered adjustable by adjustment of the bolt 1.

With the spring blade 3 mounted and stressed in the manner heretofore described, not only is the blade as a whole deformed into a dished formation, but the side arms of the blade are also curved transversely by reasonof the internal stress, and have a somewhat channel shaped'cross-sectio'n: This transversecurvature of the side arms is only slight for the greater part of the length of each arm, but is much more marked (i. e. the radius of transverse curvature is smaller) at the weakened upper sections of the blade. This is illustrated at Figs. 4 and 5, where transverse sections of the blade in the regions and BB respectively, area-shown; the plate being in its stressed condition.

With the spring blade 3 mounted and deformed in the manner described above, the mode of operationof the switch will be evident from the following brief description.

when-'thepush rod 6 is forced against the blade-=3 it--first" def lects the entire plate in the manner'ofa cantilever spring and increases the pressure between the contacts 3 and 4. As the contact.ipressurezincreases sufliciently to overcome the internal stress in the blade 3, the external forces exerted upon the blade by the operating rod 6 and the stationary contact 2 force the side arms of :the bladeto reverse their transverse curvature. This reversal oftransverse curvature takes place first at-the lower ends-of theside arms of the blade 3, because thetransversacurvature inthis region is-only slight. I As these-portions of the-side arms pass over-center and reverse-their transverse-curvature with-a snap.- action-,:: this cinternal, over-center action travels-upward :along the-.side arms 1 and forces a like over-centen-snapping action and reversal ofr-transverse curvature at;the weakenedsections BBTat the top=of1the blade: This traveling snap action, once it'is started-at the-.lowerpart of :the side arms, issselfrcompletingrwithout further rap-1 plicationzoflzthe -operating force; Thus, as soon as an over-centensnapping: action is initiated at..the-.iower parts of the .-side armspa complete reversing'zof-rtheidished formation of. the. blade 3 will take .place; 4 even :though no additional op-- erating force-is applied. By-"this actiona'itis assuredthatithe blade .is already inzmotionobefore: the-. contant .pressure-- arrives at: zero; since the initialtover centersnapping action at; :the lower parts -of-the side-.armstoccurs-before the contact pressure falls to zero. This 1 self-come pleting snapraction precludesstoppage. of the movable contact: in :a :dead. .center :position: of zero-pressure.

At Fig; 6 we have'shownra thermostatic snap acting electric switch-"embodying ;our. invention wherein thesnap acting switch .blade 3 is similar to thatshown at Figs; 1 to 5 inclusive except-that it-is-bimetallicz: The-Switchblade 3 of Fig. 6 is formed of vtwo metallic,v sheets or laminations' secured together in fixed relation,asiby-welding or thedike, withthat lamination on the side remote from the movable contactl having a greater coeflioient of: expansion than the other lamination.- The-switchshown'atFi'gJfi is provided with a heating resistor 9 in'place of'themanually operable push rod of Fig. '1, butin all other respects is similar to the switch of-Fig's..l-5,"and like-parts have been assignedthe same referencenumerals.

It will now-beunderstood that, in the operation of the device shown at Fig. 6, the bimetallic blade 3, whenfirst heated,- deflects in' cantilever fashion toward-the -fixedcontact 2. At the same time the re-entrant central arm'ia; by reason of its own similar-distortion, further tends-to increase the pressure between-thecontacts 2 and 4. When the blade' reachesa predetermined temperature, the side'armsofthe -blade,-r having a relatively slight transversecurvature, suddenly reverse their curvature due to the high expansion of the metal on the normally concaveasideof i the dished blade.

When this action occurs, the over-center reversing action is self -propelled along the length of the side arms and forces a reversal of the transverse curvature at the weakened sections BB at the top of the blade. The entire blade then reverses its dished formation, so that the high expansion lamination is on the convex side of the blade. This action causes a reversal of the angular displacement of the central arm 3a to the other side of the normal plane of the blade 3, thereby separating the contacts 2 and 4. Thus it will be evident that when the blade 3 is heated, the contact pressure is first increased, and a selfcompleting over-center snapping action is then begun at the lower part of the side arms of the blade before the contact pressure has decreased to zero. This self-completing over-center snap action ensures that the movable contact cannot be stopped in the position of zero pressure.

At Figs. 7, 8 and 9 we have shown various modified forms of over-center snap acting blades which may be utilized in snap acting devices embodying my invention. Fig. '7 shows a blade which is generally similar to that shown at Figs. 1, 2 and 6, except that the central switch arm is extended to the outer as well as the inner side of the ring and provided with a contact at each end. Fig. 8 shows another blade of generally U-shaped configuration, but in which the side arms are straight and substantially parallel rather than ring shaped as heretofore described. Fig. 9 shows a double ended form of the blade shown at Fig. 8. It will be understood that the blade shown at Fig. 9 is mounted at its center, as .by a cambered mounting bracket disposed centrally between the two side arms. It will further be understood, of course, that any of the snap acting blades shown at Figs. 7, 8 and 9 may be formed either of a homogeneous spring material such as a resilient copper alloy, or may be formed of composite metal such as the bimetallic blade heretofore described in connection with Fig. 6.

While we have described only certain preferred embodiments of our invention by way of illustration, many modifications will occur to those skilled in the art, and we, therefore, wish to have it understood that we intend in the appended claims to cover all such modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A snap action device comprising a normally fiat resilient blade formed to provide a pair of side arms and a reentrant central arm disposed in edgewise side-by-side relation and connected together at one end of said central arm, said blade having a reduced transverse section at the points of connection of said side and central arms and when unstressed lying in a normal plane with said side arms juxtaposed in a region adjacent the other end of said central arm, means for holding said side arms in cambered relation at said region and about the axis of said central arm thereby to stress and deform said blade into a dished formation and angularly displace said central arm from said normal plane, means for holding said side arms in abnormal spaced relation at said region thereby further to stress said blade, and means for inverting the dished formation of said blade thereby to reverse the angular displacement of said central arm with a snap action.

2. A snap action device comprising a normally flat resilient blade formed to provide a pair of side arms and a reentrant central arm disposed in edgewise side-by-side relation and connected together at one end of said central arm, said blade having a reduced transverse section at the points of connection of said side and central arms and when unstressed lying in a normal plane with said side arms spaced apart a predetermined normal distance in a region adjacent the other end of said central arm, means for holding said side arms in cambered relation at said region and about the axis of said central arm thereby to stress and deform said blade into a dished formation and angularly displace said central arm from said normal plane, adjustable means for holding said side arms in abnormal spaced apart relation at said region thereby adjustably to further stress said blade, the internal stress in said blade being concentrated at said reduced sections, and means for inverting the dished formation of said blade thereby to reverse the angular displacement of said central arm with a snap action.

8. A snap action device comprising a normally fiat resilient metal blade slotted to form a flat split ring and having a U-shaped re-entrant portion opposite the juxtaposed ends of said ring forming an inwardly extending arm, said ring having a reduced transverse section at each point of connection of said arm and ring and when unstressed lying in a normal plane, with said juxtaposed ends in a predetermined normal spaced relation, means for holding said juxtaposed ends in cambered relation thereby to deform said ring to a dished formation and bias said arm to a position of angular displacement to one side of said normal plane, clamping means for holding said juxtaposed ends in abnormal spaced relation thereby to concentrate internal stress in said ring at said reduced sections, and means for inverting the dished formation of said ring thereby to snap said arm to a reversed position of equilibrium oppositely angularly displaced from said normal plane.

4. A snap action electric switch comprising a base, a stationary contact mounted upon said base, a normally fiat resilient switch blade formed to provide a pair of side arms and a re-entrant central arm disposed in edgewise side-by-side relation and connected together at one end of said central arm, said blade when unstressed lying in a normal plane with said side arms juxtaposed in a region adjacent the other end of said central arm, a movable contact mounted upon said other end of said central arm, means for holding said side arms in cambered relation at said region, said holding means deforming said blade into a dished formation and angularly displacing said central arm from said normal plane with said movable contact on the convex side of said blade, and means for pressing said blade toward said stationary contact thereby to invert the dished formation of said blade and reverse the angular displacement of said central arm with a snap action.

5. A snap action electric switch comprising a base, a stationary contact mounted upon said base, a normally fiat resilient switch blade including a pair of side arms and a re-entrant central arm disposed in edgewise side-by-side relation and connected together at one end of said central arm, said blade when unstressed lying in a normal plane with said side arms in a predetermined normal spaced relation in a. region adjacent the other end of said central arm, a movable contact mounted upon said other end of said central arm, means for mounting said blade upon said base and holding said side arms in cambered relation at said region and about the axis ofrsaid; .centralsarm; saidmounting:.- means deforming said-blade into a 1 dishedgformation concave on the side remote-from.- said movable contact andangularly displacing said central arm from said normal plane, meansfor holding said side: armsnin abnormalspaced relation atlsaid regiomand means for pressingsaidblade to,- ward said stationary. contact thereby to invert the: dished formation of said bladeand-reverse the :vangular, displacement of, sa-id-v .central-rarm with a snap-action. Y

. 6. :A snap action thermostat comprising a normally flat substantially U shaped-bimetallicblade having at its bight portion a re-entrant central arm, said blade having a reduced transverse section 'at1the point of connection of each sidearm thereof with saidcentral. arm. and a when. uh.- stressed lying-in a :normal plane with the juxta: posed ends of said side arms in predetermined normal spaced relation, means forholding said juxtaposed ends incambered relation about the axis of said central arm thereby to stress and deform said blade into a dished formation, said blade when so dished having the high expansion metal on the concave side thereof and said central arm being-angularly displaced from said normalzplane-toward the convex ,side of-said blade, and meansefor holding said juxtaposed ends of said side arms inabnormalspaced relation thereby furtherto stresssaid blade, the stress .in said, blade being concentrated-at said reduced sections and said blade when heated reversing its dished formation thereby to.snap said central arm'to a reverse-position of angular displacement-withrespect to said normal plane.

7. A snap action thermostatic switch comprise ing. a base, .a fixed contact mounted uponsaid base, a normally fiat bimetallic switch: blade formed to provide a pair of,side-arms and ,a reentrant central arm disposed in edgewise sideby-side relation and connected together at one end of said central arm, said blade having a reduced transverse section atthe point of connection of each side arm thereof with the-said central arm and when unstressed lying in a normal planewith said side arms spaceduapart in a region adjacent. the-other; end. of. saidcentral arm, a movable contact mounted upon said other end of said central arm and on the low expansion side of said blade, and means for mounting said blade upon said base, said mounting means holding said side arms in cambered relation at said region and about the axis of said-central arm with the high expansion metal of said blade on the concave side thereof thereby. to deform said blade into a dished formation and angularly displace said central arm from saidnormal plane and toward the convex side of saidv blade, said blade when heated reversing its .dish formation thereby to snap said central arm to a reverse position of angular displacement. withrespect to saidnormal plane.

8. A snap action thermostaticswitch comprising a base, a fixed contact-mounted-upon said base, a normally flat bimetallic switch blade in, cluding a pair of substantially parallel side arms and a re-entrant central arm disposed in edgewise side-by-side relation and connected ,togethr at one end of said central-arm, said blade having areduced transverse section at the point of connection of each side arm thereof with the said central arm-and when unstressed-lying in a normal plane with saidside arms spaced: apart a predetermined normal .distance:ina regiorrzad+ jacent the otheraend of said central. arm-,a move able contact mounted at. said other end of said central-arm on-the low expansion side of said bladev for cooperation with said fixed contact, means for mounting said blade upon said base and holding said side arms in cambered relation atsaid region and about the axis of said centralarm, said mounting means deforming said bladeinto a dished formation with the high expansionzmetal on the concave side thereof. and angularly displacing said central arm' toward the; convex side thereof to bring said contact into engagement, and means for holding said side armsin abnormal spaced apart relation at .said region, said blade when heated first increasing the pressure between said contacts and then reversingits dished formation thereby to snap saidcentral arm to. a reverse position of angular displacement and separate said contacts 9. A snap action thermostatic switch compris inga base-,- a fixedcontact mounted upon said base, a normally flat bimetallic switch blade formed to provide a pair of side arms and a substantially U.-shaped re-entrant central arm dispised-in edgewise'side-by-side relation and connected together at-the open end of said central arm, said blade having. reduced transverse sections atthe open ends of said central arm and wherrunstressed lying in a normal plane with saidzsidearms in predetermined normal spaced relation adjacentthe other end of said central arm, a movable contact mounted upon said othe eraend of saidcentral arm at the low expan-, sion side .of said blade for cooperation with said fixed contact, means for mounting said blade upon'saidbase and holding said side arms in cambered relation at -said region and aboutthe axiszofsaidcentralarm, said mounting means deforming said blade into a dished formation with the high expansion metal of said blade on the concave side thereof and angularly displacing said central arm toward the convex side thereof to bring said contacts into engagement, and means for holding said side arms in abnormal spaced relation at said region thereby further to stress said blade, said blade when heated first increasing the pressure between said contactsand then reversing its dished formation to snap. said centralarm to. a reverse positionof angular displacement thereby to separate said contacts.

10. A snap action thermostatic switch comprising a base, a fixed contact mounted upon said base, a normally flat bimetallic switch blade formed to provide a pair of side arms and a substantially U-shaped re-entrant central arm disposedin edgewise side-by-side relation and connected together. at the open end of said central arm, said blade having reduced transverse sections at the points of connection of said central arm with said side arms and when unstressed lying in a normal plane with saidside arms spaced apart a predetermined normal distance in a region adjacent the other end of said centralarm, a movable contact mounted upon-said other end of said' central arm at the low expansion side of said-bimetallic blade, means for ,mounting said blade upon said baseand holding said side arms in cambered relation at said region and about the axis of said central arm, said mounting means deforming said blade into a =dishedformation with the high expansion metal'on the concave side thereof and angularly displacing said central. arm from said normal plane toward .the convex side of said blade'to hold-isaid1c1contacfs: irrengagement, and adjustablea-meansr holding-said side arms in abnormal spaced apart relation at said region thereby adjustably to further stress said blade and con centrate deformation of said blade at said reduced sections, said blade when heated first deflecting to increase the pressure between said contacts and then reversing its dished formation to snap said central arm to a reversed position of angular displacement and separate said contacts.

11. A snap action thermostatic switch comprising a base, a fixed contact mounted upon said base, a normally flat substantially U-shaped bimetallic switch blade having at its bight portion a substantially U-shaped re-entrant central arm, said blade having reduced transverse sections at the points of connection of said central arm with the side arms of said blade and when unstressed lying in a normal plane with the juxtaposed ends of said side arms spaced apart a predetermined normal distance, a movable contact mounted upon the inner end of said central arm at the low expansion side of said blade, means for mounting said blade upon said base and holding said juxtaposed ends of said side arms in cambered relation thereby to deform said blade into a dished formation, said blade when so dished having the high expansion metal thereof on the concave side with said central arm angularly displaced from said normal plane toward the convex side to bring said contacts into engagement, and adjustable means for holding the juxtaposed ends of said side arms in abnormal spaced apart relation thereby to concentrate deformation of said blade at said reduced sections, said blade when heated first deflecting to increase the pressure between said contacts and then reversing its dished formation to snap said central arm to a reverse position of angular displacement and separate said contacts.

12. A snap action thermostatic switch comprising a base, a fixed contact mounted upon said base, a normally fiat bimetallic switch blade formed as a split fiat ring having a substantially U-shaped re-entrant arm opposite the juxtaposed ends of said ring, said ring having weakened sections at its points of connection to said re-entrant arm and when unstressed lying in a normal plane with said juxtaposed ends in predetermined normal spaced relation, a movable contact mounted upon the inner end of said arm on the low expansion side of said blade, means mounting said blade upon said base and holding said juxtaposed ends in cambered relation, said mounting means deforming said ring to a dished formation with the high expansion metal on the concave side thereof and biasing said arm to a position of angular displacement toward the con vex side of said deformed ring, and adjustable means for holding said juxtaposed ends of said ring in abnormal spaced relation thereby to concentrate internal stress in said ring at said reduced sections, said blade when heated first defleeting to increase the pressure between said contacts and then reversing its dished formation to snap said arm to a reverse position of angular displacement and separate said contacts.

13. A snap action thermostat comprising a normally flat bimetallic blade formed to provide a pair of side arms and a re-entrant central arm disposed in side-by-side relation and connected together at one end of said central arm, said blade having a reduced transverse section at the point of connection of each of the said side arms with the central arm and when unstressed lying in a normal plane with said side arms spaced apart a predetermined normal distance in a region adjacent the other end of said central arm, means for holding said side arms in cambered relation at said region and about the axis of said central arm thereby to stress and deform said blade into a dished formation and angularly displace said central arm from said normal plane, and adjustable means for holding said side arms in abnormal spaced apart relation at said region thereby adjustably to further stress said blade, said blade when changed in temperature a predetermined amount inverting its dished formation thereby to reverse the angular displacement of said central arm with a snap action.

JAMES A. SPINA. EDWARD O. ANDERSEN.

REFERENCES CITED The following references are of record in the 

